An automatic gain control device computes average power from an I signal component and a Q signal component of an input signal, and controls gain by which the input signal is multiplied according to the average power. The automatic gain control device adjusts signal power of the input signal to a predetermined range of signal power by controlling the gain. Processing of automatic gain control is used by many electronic devices, and is also called AGC (auto gain control) generally.
As the automatic gain control device using the conventional AGC, Patent Document 1 is known. The automatic gain control device shown in Patent Document 1 computes a received level of digital data of an AD converter output, and determines that an AD converter is in an overflow state when a computed value of the received level is more than or equal to a threshold value. When the overflow is detected, the automatic gain control device controls a gain variable amplifier based on a predefined predetermined value without using a received level ratio computed based on a received level average value.